Semiconductor storage devices such as a NAND flash memory have been downscaled to increase storage capacity. Development of memories using new materials is progressing to achieve further downscaling. Novel memories such as a resistance random access memory (ReRAM), a phase-change RAM (PRAM), a phase-change memory (PCM), an interfacial PCM (iPCM), a ferroelectric NAND-type memory (FeNAND), and a magnetic random access memory (MRAM) are developed.
Among these novel memories, the PCM and the iPCM are brought to a low resistance state (a set state) or a high resistance state (a reset state) according to phase transition of a phase-change film of the relevant memory cell. This enables the PCM and the iPCM to store therein logical data.
In the PCM and the iPCM, in some cases, an operation called “slow cooling” of slowly sinking a voltage applied to the memory cell is required to rewrite a Reset state with a Set state.
If a voltage applied to the memory cell is rapidly sunk in these cases, it is possible that the memory cell remains as the Reset state without changing from the Reset state to the Set state or returns to the Reset state even when it is temporarily changed to the Set state. On the other hand, in order to rewrite the Set state with the Reset state, it is considered that a “rapid cooling” operation of rapidly sinking a voltage applied to the memory cell is required. As described above, in the PCM and the iPCM, a control on a decrease rate of a write voltage is demanded when application of the voltage is to be stopped.